The vitamin C question

Dr Ioannis Mavromichalis

This is a quite old question, which has yet to receive a definitive
answer! Despite the fact that pigs, like most animals (excluding humans,
primates, and guinea pigs), can readily synthesise enough vitamin C to cover
their requirements, many manufactured diets and premixes contain large
concentrations of this vitamin. Let's explore this issue a bit
furtherâ€¦

This is a quite old question, which has yet to receive a definitive answer!
Despite the fact that pigs, like most animals (excluding humans, primates, and
guinea pigs), can readily synthesise enough vitamin C to cover their
requirements, many manufactured diets and premixes contain large concentrations
of this vitamin. Let's explore this issue a bit furtherâ€¦

Vitamin C
(ascorbic acid or ascorbate) is a naturally-occurring metabolite of glucose. The
absence of the enzyme L-gulonolactone oxidase promotes vitamin C to the status
of a dietary essential nutrient for only a few mammalian species.

Also, vitamin C is thought to
play a significant role in the functionality of the immune system. During
periods of stress (e.g., excessive heat, disease challenge, fighting, crowding)
body stores of vitamin C are depleted, and high concentrations of vitamin C
metabolites are excreted in urine.

SynthesisingPigs are able
to synthesise vitamin C as early as their first week of age, whereas large
quantities of vitamin C are present in sow's colostrum and milk.

However, weaning at an age of 14 to 28 days imposes an immense
nutritional, social, and environmental stress on pigs. In fact, the plasma
concentration of vitamin C drops drastically in pigs shortly after weaning. This
has been taken as evidence of either an insufficient biosynthesis rate and (or)
an increased requirement for vitamin C.

Weight gainIn a study
conducted in the 80s, pigs weaned at 4 weeks of age were offered diets fortified
with increasing concentrations of vitamin C (0, 330, 660, and 990 mg/kg) in a
28-day growth assay. Overall, weight gain was improved by 17% and feed intake by
13% in pigs offered the vitamin C-fortified diets.

Following this unique
study, a number of experiments were conducted in several institutions worldwide
to verify and refine the effects of supplementation with vitamin C, but with
limited success as results have been mixed and ambiguous.

In most
studies, fortification of nursery diets with ascorbic acid at various levels
ranging from as little as 75 to as much as 990 mg/kg did not result in enhanced
growth performance, haemoglobin concentration, immunity, or survivability. Also,
injections with vitamin C (40 mg/kg every other day) did not enhance growth
performance. Other trials, largely unpublished, showed some limited
response.

Crowded or stressed pigs benefit?It has been
suggested that pigs crowded or stressed by cold temperatures may benefit from
vitamin C supplementation. To test this hypothesis, a large study involving 11
experimental stations and 1,296 nursery pigs was conducted without any
significant response to dietary vitamin C supplementation (625
mg/kg).

Vitamin C is sensitive to a variety of environmental factors
including heat, oxygen, and alkalinity. It has been proposed that the lack of
response observed in these experiments was due to inevitable vitamin C losses
that occurred during storage and feeding.

However, in most of the
experiments, the researchers were aware of this problem and they tried to avoid
considerable vitamin losses by frequent preparation and cool storage of the
diets.

Interestingly, in recent studies, the use of more stable forms of vitamin C
(magnesium-L-ascorbyl-2-phosphate and L-ascorbyl-2-polyphosphate) did not help
in eliciting a constant and repeatable positive growth response in segregated or
early-weaned pigs.

Limited evidenceToday, there is some
limited evidence suggesting that supplemental ascorbic acid might be beneficial
during stress in certain species (e.g., humans, chickens). However, in pigs
there are no solid data to suggest such a beneficial effect.

There are, indeed, some research reports that suggest
trends toward increased growth performance in nursery pigs offered vitamin
C-fortified diets, but these trends have not been statistically significant
(P>0.05). In fact, it is somewhat difficult to explain most of
these trends because they are neither repeatable nor biologically justified.

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One comment

Gino Totte Panagro health & nutrition

8 May 2008 15:35

Is a pig geneticly still able to produce vitamin C?Is there always enough glucose available for vitamin C production?Is vitamin C important in white blood cells?In these trials did pig have or have not infections and what kind of infections did they have?Vitamin C is an antioxidant and will do it's job if there is not enough vitamin C available for optimal health (to protect cells from oxidation). If there is enough vitamin C production in the pig then there won't be any difference in a trial between groups with no added vitamin C en groups with added vitamin C. But if vitamin C production is to low to support optimal health and if we make pigs on purpose ill in a trial and then we make a difference in groups with added vitamin C then you will see results. The only problem is to estimate if a pig can produce enough vitamin C or not. Another problem is finding finance to pay for trials. Margin on vitamins has always been low so big companies which produce vitamin C with no patent were not interested in research on this subject.